This invention relates to an adjustable gauge steering axle particularly intended for two-wheel drive agricultural tractors, being of a type which comprises an adjustable length beam and a steering control associated with said beam and including a double-acting, dual piston rod hydraulic cylinder with either piston rods active on a corresponding steering arm through a respective strut.
An axle having these features is known from Massey Ferguson France, a French corporation.
This prior axle has a steering control which includes a double-acting, dual piston rod hydraulic cylinder, the two piston rods whereof, which juts out of the hydraulic cylinder body from opposed axial ends thereof, are each provided with a telescoping extension whereby they are connected to a respective one of the steering arms. Each steering arm is made, in turn, fast rotatively with a spindle carrying the wheel hub. The piston rods of the hydraulic cylinder, in combination with their extensions, will behave, therefore, as a single, rigid straight bar which is adjustable telescopically to accommodate gauge changes and interconnects the steering arms.
In consequence of the geometry of the steering arms and the spindles (which would normally lie at an angle from vertical) the hydraulic cylinder is swivel connected to the axle beam by means of a pivot having its axis parallel to the beam and of a swivel joint intervening between said pivot or kingpin and the cylinder body.
Accordingly, the hydraulic cylinder will move, on operation of the steering system, toward and away from the axle beam and oscillate both about the kingpin and the swivel joint.
This axle configuration has a major drawback in that it is high in volume requirements due to the positioning and shifting capability of the hydraulic cylinder. Such volume requirements are sometimes in conflict with the positioning of other components of an agricultural tractor, which makes the axle unsuited to fill specific demands for compactness.
Another example of an adjustable gauge axle is described in French Patent No. 2,173,517. The axle of this prior patent has a steering control which includes a double-acting, dual piston rod hydraulic cylinder wherein the piston rods act on their corresponding steering arms through respective rigid struts and are extensible telescopically to the desired gauge dimension. Understandably, the strut length would be settled by the sizing of the steering control and the axle in the narrowest gauge condition; consequently, the struts will be somewhat short compared to the length of the piston rods, with the latter extended telescopically to provide intermediate or widest gauge dimensions. The reduced length dimension of the struts relatively to the piston rods, especially with an axle designed for tight steering angles, is a source of increased stress on the piston rods tending to bend them. This flexural stress results eventually in unacceptable wear of the seals active on each piston rod of the steering control. This problem is made more serious by that, on account of the telescoping design of interest, the piston rods are constructed tubular, at least in part, and hence weaker than conventional rods.
With other fixed gauge axles (front axles for four-wheel drive tractors), known from this Applicant's production, the volume problem has been addressed by affixing the double-acting, dual piston rod hydraulic cylinder of the steering control to the axle beam and interposing a swivel joint between each piston rod and its respective strut connecting it to the steering arm.
In this way, the cylinder could be brought nearer the axle beam, locating it at an offset location from the line of action of the steering arms; however, the axle allows for no gauge adjustment.